Several different types of magnet structures are known that have the above construction. U.S. Pat. No. 5,555,251 discloses a magnet structure which has two pole pieces having a massive ferromagnetic layer and a layer made of laminated ferromagnetic foils or sheets. In this arrangement, sheets are made of one piece and have a number of radial cuts, arranged from a center of the sheet. The sheets have a circular shape, coaxial with the center around which the cuts are radially arranged. All the sheets have the same shape and the same pattern of cuts.
The cuts of each sheet are offset with respect to an adjacent sheet by rotating each sheet relative to the adjacent sheet by an angle smaller than the angular distance between two successive radial cuts.
As a result, in order to form the laminated layer of each pole piece, the sheets must be properly offset before being bonded together by an adhesive layer or an electric insulating and adhesive layer which coats the sheets. While the assembly of the laminated layer is intrinsically simple, it is still dependent on the position of the sheets relative to each other, and this is a parameter to be accounted for during manufacture of the pole pieces. Moreover, this may generate errors in the angular positioning of the sheets.
Also, due to the one-piece construction of the sheets, handling problems may arise when the sheets, as well as the pole pieces have a relatively large size. An additional problem consists in that that the sheets that require a high dimensional precision and are made of a special magnetically permeable material are generally not fabricated of sufficiently large sizes, and any size increase thereof would involve a considerable cost increase. In this case, the provision of one-piece sheets is not feasible or involves higher costs for the magnet structure.
The invention is based on the problem of providing a magnet structure as described hereinbefore which, thanks to simple and inexpensive arrangements, allows easier handling, particularly for the fabrication of large-sized magnets, and helps to obviate the above drawbacks.